MR-guided focused ultrasound (MRgFUS) is a promising non-invasive technique for cancer therapy, neural tissue ablation, and drug delivery across the blood brain barrier [1,2]. Real time MR thermometry of the heated volume, which can be based on the proton-resonance frequency (PRF) shift [3], can be an aspect of these procedures. Early work in the field focused on 2D imaging, either of one slice or a small number of slices; however, the desire to monitor the entire sonicated volume has led the field towards the development of rapid, 3D methods [4]. Acquiring fully sampled 3D volumetric data to measure phase changes due to the PRF shift in response to heating is time consuming, however, and so it is desirable to develop accelerated methods in order to meet the spatial and temporal requirements for adequate monitoring of thermal therapy.
The data acquisition efficiency of spiral trajectories can be higher than that of Cartesian scanning. Therefore, spiral trajectories are an attractive way in which to improve temporal resolution while maintaining spatial resolution in MR thermometry [5]. Additionally, spirals can have good robustness in the presence of motion and, for MRgFUS, off-resonance may not cause a shift in the position of the hot-spot as it does for EPI-based methods. Further speed-ups can be gained by utilizing the large amount of static spatial information present in the series of thermal maps. The Kalman filter method can use a statistical model improve a series of temporal images and has been successful in acceleration of myocardial imaging [6], and can provide real time feedback in MRI thermometry [7]. Accelerated thermometry with a 3D spiral acquisition and Kalman filter reconstruction may provide significant advantages.
It is with respect to these and other considerations that the various embodiments described below are presented.